This invention relates to perfluoroaminoether polymers and to a process for preparing them. In particular, there are described new perfluoroaminoether polymers, and the process for preparing them, which are obtained by copolymerization of fluorinated olefins with oxaziridines, in particular in the presence of ultra-violet radiations or of chemical initiators.
The new perfluoroaminoether polymers of the present invention contain the perfluoroaminic units statistically distributed along the polymeric chain.
Tertiary amines containing in their chain perfluoroalkyl groups bound by ethereal oxygen atoms are known.
For example, U.S. Pat. No. 3,882,178 relates to fluorinated tertiary amines containing ethereal bonds, prepared by reacting non-fluorinated aminoalcohols with tetrafluoroethylene and subsequent electrochemical fluorination. In this case, however, the aminic groups are present only as polymer end groups.
U.S. Pat. No. 3,997,607 teaches how to prepare aminoethers by electrochemical fluorination of the reaction product of a tertiary amine having hydroxyethyl groups with hexafluoropropene.
European patent application No. 214,852 teaches how to prepare perfluoroaminoether products characterized by 2 or 3 tertiary aminic nitrogen atoms as end groups, bound to perfluoropolyethereal units of type --C.sub.2 F.sub.4 --O--C.sub.2 F.sub.4 or of type: ##STR1## said products being obtained by electrochemical fluorination of the corresponding partially hydrogenated precursors.
However, also these products possess the units containing N as end groups, as mentioned above with reference to U.S. Pat. No. 3,888,178.
The products of the present invention cannot be considered as perfluoroethers having perfluoroalkylaminic groups as end groups, but polymers characterized by repeating units distributed at random in the chain, such as, for example: ##STR2##
Furthermore, the process for preparing the polymers of the present invention does not regard the electrochemical fluorination of hydrogenated compounds, but the reaction of. perfluoroolefins with perfluorooxaziridines in the presence of ultra-violet radiations or, as an alternative, in the presence of proper chemical initiators or starter compounds acting as a catalyst, such compounds being selected among peroxy compounds and perfluoroalkyl radical generators.
U.S. Pat. No. 4,287,128 describes the preparation of oxaziridines of type: ##STR3## generally discussing the possibility of polymerizing these compounds, without giving, however, any specific indication on the polymerization or copolymerization of the oxaziridines.
The article by B. O. Brien, W. Lam and D. D. Desmarteau in J. Org. Chem. vol. 51, No. 3, 1986, contains an exhaustive study on the reactivity of oxaziridine: ##STR4## towards various 1,1-difluoroolefins.
According to the results of such study, the above-described oxaziridine does not polymerize, but provides cycloaddition products with most of the 1,1-difluoroolefins, so forming perhalo-1,3-oxazolidines.
For example, by means of an 18-hour heat-treatment at 55.degree.-100.degree. C., from an equimolecular amount of CF.sub.2 .dbd.CF.sub.2 and oxaziridines of type: ##STR5## it is possible to obtain, with a satisfactory yield (60%), a cyclic product, i.e. perfluoro-3-methyloxazolidine, and no traces of oil, namely of polymer. Conversely, the reaction of: CF.sub.3 CF.dbd.CF.sub.2 with ##STR6## at 150.degree. C. for 18 hours does not provide traces of oxazolidine and exhibits the formation of a non-volatile oil.
Thus, polymers obtained from oxaziridines do not result to be described or inferable from the prior art.
The Applicant has surprisingly found that it is possible to prepare polymers with perfluorinated olefins if a specific process is utilized, in particular if the polymerization reaction is conducted during suitable stretches of time in the presence of UV radiations, having a wave-length ranging from 2000 A.degree. to 6000 A.degree. , or, as an alternative, in the presence of suitable starters chosen among peroxy compounds and perfluoroalkyl radicals generators of precursors.
Thus, an object of the present invention are perfluoroaminoethers having the following general formula: ##STR7## wherein R.sub.f and R'.sub.f, like or different from each other, represent: ##STR8##
a, b, are integers and c an integer or zero;
a+b+c.gtoreq.2
a=1
c.gtoreq.0
said repeating units being like or different and statistically distributed along the polymer chain;
Z represents F or ##STR9## or a C.sub.1 -C.sub.10 perfluoroalkyl group;
R represent F or a C.sub.1 -C.sub.10 perfluoroalkyl group, like or different from Z;
X and Y:
a) when at least one of R and Z is different from F, represent F and CF.sub.3, so that if X=F is Y=CF.sub.3 or viceversa and c=0, or represent both F:
b) when R=Z=F, X represents F and Y represents a perfluoroalkyl C.sub.1 -C.sub.5 group or viceversa and c=0, or represent both F.
When relatively low molecular weight polymers are obtained, e.g. ranging from 450 to 20.000 about, and in particular from 600 to 5000 about, there is approximately:
2.ltoreq.a+b+c.ltoreq.200
1.ltoreq.b+c.ltoreq.50
0.ltoreq.C.ltoreq.100.
While in the case of higher molecular weight polymers, aprroximately there is c&gt;a and, e.g. 50.ltoreq.b+c/a.ltoreq.100, with a
.DELTA.H crystallization factor comprised between 5 and 70 about, expressed as Joules/g.
The perfluoroaminoethers of the present invention are prepared by reaction of oxaziridines of formula (1): ##STR10## wherein each R represents F or a perfluoroalkyl group having from 1 to 10 carbon atoms and R' is F or the group: ##STR11## or a perfluoroalkyl group having from 1 to 10 carbon atoms, with a perfluoroolefin chosen between perfluoropropene and perfluoroethylene, at temperatures ranging from -80.degree. C. to 120.degree. C. in the presence of ultra-violet radiation having a wave-length from 2000 to 6000 A.degree.. Preferably, the temperature ranges from -50.degree. to +50.degree. C.
Among the oxaziridines described, particularly preferred is 2-(trifluoromethyl)-3,3-difluoro-oxaziridine (II): ##STR12## or 2-(trifluoromethyl)-3-(N,N-bis-trifluoromethyl)-oxaziridine (111): ##STR13##
The oxaziridines constituting the starting materials of the present invention are known compounds and are preparable according to the methods described in the already cited U.S. Pat. No. 4,287,128 or by Falardeau, Desmarteau, J. Am. Chem. Soc. 1976, 98, 3529 or in Italian patent application No. 22,576 A/87 in the name of the Applicant hereof.
As it is known, the reaction time is a function of the other reaction parameters and it is generally of about 1-24 hours.
As already mentioned hereinbefore, in order to obtain the polymerization which is the object of this invention, it is necessary to have a combination of the above-indicated temperature and UV radiation values.
A further object of the present invention is an alternative process for preparing the above-described perfluoroaminoethers, which comprises a thermal treatment of said perfluoroolefins at a temperature of from 0.degree. to 200.degree. C. in the presence of catalytic amounts of a chemical starter or initiator selected among peroxy compounds and perfluoroalkyl radical generators.
Such chemical starters or initiators must be able to start polymerization of the perfluoroethylene by giving rise to free radicals (peroxy compounds) or by decomposing themself at the reaction temperature in perfluoroalkyl radical (perfluoroalkyl radical generators).
The peroxy compounds used in the present invention and the teachings useful to the preparation of same are well known; in particular they are described in the already cited publication by Falardeau, Desmarteau J. Am. Chem. Soc. 1976, 98, 3529.
For example, it is possible to use peroxides such as CF.sub.3 --NH--CF.sub.2 --O--OCF.sub.3.
The perfluoroalkyl radical generators, used according to the invention, are per se known compounds. They are described for instance, in E.P. No. 121,898 and in italian pat. appln. No. 20,061 A/87.
While no limit was found as to composition of the generated perfluorinated radicals, radicals containing up to 6 carbon atoms have shown operative.
For example, if is possible to use perfluoroalkyl radicals generators such as: ##STR14##
As above mentioned, the chemical precursor (peroxy or perfluoroalkyl radical generator compounds) are employed in catalytic amounts comprised e.g. between 0.5% and 5% by weight in respect of the reaction mixture.
As to reaction pressure it is possible to operate at atmospheric or higher pressure, if necessary, for example as high as 50 atm.
When the oxaziridine (II) is employed, the perfluoroolefin reactant may be a perfluoroolefin of formula: EQU R" FC=CF.sub.2
wherein R" is F or a perfluoroalkyl group having 1 to 5 carbon atoms.
Finally the processes above shown can also be carried out by operating in a suitable solvent, e.g. chosen among chlorocarbon solvents.
The perfluoroaminoethers of the present invention exhibit characteristics of high chemical inertia and high thermal stability, which render them particularly useful as lubricating oils, molding polymers. In particular, such oils, thanks to the low pour point values obtainable (ranging from -5.degree. C. to -90.degree. C.) and to the narrow boiling point range, can be utilized also as fluids for the vapor or liquid phase heating in the electronic industry.